Present day RF radio receivers must be capable of detecting and demodulating RF signals in which the desired information signal is often much weaker than existing interfering signal. Recently, receivers which directly convert the RF signal to a much lower frequency have been developed. The RF signal is down-converted to a zero-IF or low-IF intermediate frequency where analog and/or digital signal processing is more efficient. Present day radio receivers typically employ real filters to filter out interfering signals, and amplifiers to increase the level of the desired signal. If real filters are used in a LIF path they have the disadvantage of not differentiating between negative frequencies and positive frequencies, hence a high performance image reject mixer is typically used to separate the positive/negative frequencies. In addition, where the frequency of the interfering signal is close to the frequency of the desired signal in a LIF architecture, a substantial number of filter poles are required to filter out the interfering signals and the overall amplifier circuit is such that considerable power is required to amplify the desired signal to an appropriate level for demodulation. In addition, DC offsets caused by both circuit imperfections and characteristics inherent in certain forms of modulation must be removed since they can be several orders of magnitude larger than the desired signal and can degrade the performance of the final demodulator circuit.
Therefore, there is a need for a simpler architecture for enhancing the gain performance and removing DC offsets while minimizing power consumption.